Sensorless motor drives are used in a variety of applications, particularly where providing position and/or speed sensors directly at a motor load is difficult or impractical. A typical sensorless system employs a voltage-frequency (V/F, alternatively known as Volts per Hertz, V/Hz) controller providing a voltage setpoint according to a desired motor speed or frequency, and this form of sensorless control has been used primarily with induction motors. In certain applications, a step-up transformer may be used to boost the motor drive output voltage, allowing use of a low-voltage drive to power a medium voltage induction motor, and/or to reduce I2R losses and facilitate use of a smaller diameter cable wire for long cable runs between the motor drive and the driven motor. Certain applications also employ sine wave filters, such as LC filters to suppress reflected wave voltage spikes associated with pulse width modulated (PWM) variable frequency drives. Use of sensorless voltage-frequency control techniques, however, may lead to problems, particularly where a transformer and/or sine wave filter is connected between the motor drive and the motor load. Conventional sensorless field-oriented-control (FOC) or other open loop speed control techniques have thus been found generally unsuitable for low-speed motor drive operation where output filters and transformers are used, such as in electric submersible pumps (ESPs), and these difficulties are particularly problematic in driving permanent magnet synchronous motors (PMSMs). Moreover, voltage-frequency control in combination with a sine wave filter under starting conditions may result in the motor not being able to start, with large oscillations on the rotor shaft for low frequency commands. Motors in sensorless speed control applications also suffer from oscillation in rotor velocity about the setpoint speed following load transitions or speed setpoint adjustments, particularly at low speeds. In certain situations, moreover, the driven motor may be unable to successfully start from a stopped condition due to unstable motor speed oscillations. Thus, improved techniques and motor drives are needed for sensorless motor speed control, particularly for driving permanent magnet motors to provide improved stability control.